Both audio and ultrasonic technologies are being used in mobile electronic devices, such as smartphones and tablets. On top of the “classical” use of audio speakers to enable hands-free operation, consumers today expect higher-quality audio and video performance, and thus higher performance requirements from audio speakers in smartphones and wearable devices. Ultrasonic-enabled applications include stylus-based inputs either on-screen or on a nearby desktop, touch-less interfaces such as gestures to perform commands, proximity sensors etc.